The present invention relates generally to polymerizable compositions useful for bonding low surface energy substrates. Also disclosed are polymerizable compositions and bonding compositions prepared therefrom, a kit comprising the polymerizable composition, coated substrates prepared therefrom, bonded articles prepared therefrom, and methods of preparing such bonded articles. In particular, the polymerizable compositions comprise monomer blends comprising certain ethylenically unsaturated monomers.
An efficient, effective means for adhesively bonding low surface energy plastic substrates such as polyethylene, polypropylene and polytetrafluoroethylene (e.g., available under the trade designation, TEFLON from E. I. DuPont de Nemours; Wilmington, Del.) has long been sought. The difficulties in adhesively bonding these materials are well known (See, for example, xe2x80x9cAdhesion Problems at Polymer Surfacesxe2x80x9d by D. M. Brewis that appeared in Progress in Rubber and Plastic Technology, vol. 1, p. 1 (1985)).
Conventional bonding approaches often use complex and costly substrate surface preparation techniques, such as flame treatment, corona discharge, plasma treatment, oxidation by ozone or oxidizing acids, and sputter etching. Alternatively, the substrate surface may be primed by coating it with a high surface energy material. However, to achieve adequate adhesion of the primer, it may be necessary to first use the surface preparation techniques described above. All of these techniques are well known, as reported in Treatise on Adhesion and Adhesives (J. D. Minford, editor, Marcel Dekker, 1991, New York, vol. 7, pp. 333 to 435). The known approaches are frequently customized for use with specific substrates. As a result, they may not be generally useful for bonding low surface energy substrates.
Moreover, the complexity and cost of the presently known approaches do not render them particularly suitable for use by the retail consumer (e.g., for home repairs, do-it-yourself projects, etc.) or by low-volume operations. One vexing problem is the repair of many inexpensive everyday household articles that are made of low surface energy materials. Examples of such household articles are trash baskets, laundry baskets, toys, etc.
Consequently, there has been a considerable and long felt need for a simple, easy to use adhesive that can readily bond a wide variety of substrates, especially low surface energy materials, such as polyethylene, polypropylene and polytetrafluoroethylene, without requiring complicated surface preparation, priming and the like.
While an adhesive that can bond low surface energy substrates is certainly advantageous, the commercial utility of such an adhesive would be enhanced if the components thereof could be combined in a convenient mix ratio. This would permit easy application of the adhesive using conventional adhesive dispensers without the need for laborious hand weighing and mixing of the different components. However, the convenient mix ratio should not come at the expense of significantly reduced storage stability or performance. Thus, there is not only a need for an adhesive that can bond low surface energy substrates, but for such an adhesive that can be readily blended in a convenient mix ratio.
It may be desirable for such adhesives to possess other attributes. For example, polymerizable acrylic adhesives are often associated with a strong and unpleasant odor. While not affecting performance, the odor may discourage some people from using these adhesives and encourage them to select other alternatives. In addition, for certain situations, it may be desirable to utilize adhesives that have decreased irritation-potential (e.g., skin and respiratory irritation). In general, low molecular weight (i.e., molecular weights of 140 or less) acrylate monomers are known to be potentially irritating to the user.
Polymerization of ethylenically unsaturated monomers is well known. For example, Ritter (U.S. Pat. No. 4,385,153) discloses single-component mixtures of aerobically-hardening adhesives containing: (1) polymerizable olefinically-unsaturated compounds having a molecular weight of between 63 and 10,000; (2) at least one organoboron compound capable of initiating the polymerization thereof in the presence of oxygen; and (3) at least one compound capable of inhibiting and/or stabilizing anionic polymerization. The adhesives are useful for bonding metal, wood, glass, ceramic material, and plastics, as well as in dentistry and surgery.
Two-part initiator systems useful in preparing acrylic adhesive compositions are also known. For example, see Skoultchi (U.S. Pat. No. 5,286,821). Skoultchi discloses two-part initiator systems useful for preparing acrylic adhesive compositions. The systems include a stable organoboron amine complex and an aldehyde destabilizer. The adhesive compositions are reportedly particularly useful in structural and semi-structural applications, such as speaker magnets, metal-metal bonding (automotive), glass-metal bonding, glass-glass bonding, circuit board component bonding, selected plastic to metal, glass, wood, and electric motor magnets. Those plastics that may be bonded are not further described. See also Skoultchi et al. (U.S. Pat. Nos. 5,106,928 and 5,310,835).
Polymerizable compositions useful for bonding low surface energy substrates have been reported only recently, for example, by Zharov et al. (U.S. Pat. No. 5,539,070). Zharov et al. generally disclose polymerizable acrylic monomer compositions made with polymerization systems based on organoborane amine complexes. Particularly preferred monomers are stated to be blends of alkyl acrylates (e.g., butyl acrylate) and alkyl methacrylates (e.g., methyl methacrylate).
Pocius (U.S. Pat. No. 5,686,544) discloses organoborane polyamine complex initiator systems and polymerizable compositions that are capable of forming polyurethane/polyurea acrylic adhesives that have exceptionally good adhesion to low surface energy polymers, such as polyethylene, polypropylene, and polytetrafluoroethylene. Acrylic monomers are generally disclosed therein as useful for the reaction. It is stated, however, that the most preferred monomers include lower molecular weight methacrylate esters such as methyl methacrylate, ethyl methacrylate, methoxyethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, and blends thereof. It is also stated that preferred monomers are blends of lower molecular weight alkyl methacrylate esters (e.g., methylmethacrylate) and C4-C10 alkyl acrylates (e.g., butylacrylate). Similar systems are disclosed in Pocius (U.S. Pat. Nos. 5,616,796 and 5,621,143). While the foregoing polymerizable compositions may be useful for bonding low surface energy substrates, one disadvantage thereof is the relatively high odor of the exemplified compositions.
It would be desirable to provide new compositions that are polymerizable to compositions that can be used to bond low surface energy substrates. Most preferably, it would be desirable to provide compositions that have relatively low odor, as compared to conventional compositions.
Polymerizable compositions for use with an aerobic initiator comprise a monomer blend comprising:
a first ethylenically unsaturated monomer; and
a second ethylenically unsaturated monomer, wherein the monomer blend has an average boiling point of at least about 160xc2x0 C., and an average monomer fluorophilicity of at least 3.25, and wherein the monomer blend is polymerizable to a polymer having a glass transition temperature of at least about xe2x88x9220xc2x0 C.
Such compositions are advantageously less odorous than monomer blends previously exemplified for used when bonding low surface energy substrates. To further reduce the odor of the compositions, preferably the average boiling point of the monomer blend is at least about 190xc2x0 C., more preferably at least about 210xc2x0 C. This enables more user-friendly adhesives. To further enhance user-friendliness, it is preferred that at least one, more preferably both, of the ethylenically unsaturated monomers, is a methacrylate monomer when (meth)acrylate monomers are used.
Such compositions typically enable adequate bonding to low surface energy substrates, preferably to at least two different low surface energy substrates, and more preferably to at least three different low surface energy substrates. Exemplary low surface energy substrates include: polypropylene (PP), polytetrafluoroethylene (PTFE), and high-density polyethylene (HDPE). Most preferably, a particular adhesive prepared therefrom is able to adequately bond PTFE with an overlap shear bond strength of at least about 300 psi (4.14 MPa), HDPE with an overlap shear bond strength of at least about 700 psi (4.83 MPa), and PP with an overlap shear bond strength of at least about 800 psi (5.52 MPa).
To enhance such bonding performance, it is preferred that the monomer blend has an average monomer fluorophilicity of at least about 3.50. Also, it is preferred that the monomer blend is polymerizable to a polymer having a glass transition temperature of about 20xc2x0 C. to about 80xc2x0 C.
With respect to specific preferred monomer components, the monomer blend comprises: 10-90 wt. % M1,25-70 wt. % M2, and 0-65 wt. % M3 based on total eight of the monomer blend, wherein:
M1 is tetrahydrofurfuryl methacrylate; M2, is one or more monomers selected from the group consisting of 2-ethoxyethyl methacrylate, n-hexyl acrylate, cyclohexyl methacrylate, isooctyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and isobornyl acrylate; and M3 is one or more monomers selected from the group consisting of isobutyl methacrylate, n-butyl methacrylate, cyclohexyl acrylate, n-hexyl methacrylate, isobornyl methacrylate, and isodecyl methacrylate.
With respect to even more preferred monomer components, M2 is one or more monomers selected from the group consisting of 2-ethoxyethyl methacrylate, cyclohexyl methacrylate, isooctyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and isobornyl acrylate, and M3 is one or more monomers selected from the group consisting of n-hexyl methacrylate, isobornyl methacrylate, and isodecyl methacrylate. Most preferably, M2 is one or more monomers selected from the group consisting of 2-ethoxyethyl methacrylate, isooctyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and isobornyl acrylate, and M3 is one or more monomers selected from the group consisting of isobornyl methacrylate and isodecyl methacrylate.
The polymerizable compositions are useful in kits that comprise the polymerizable composition and an initiator component for polymerizing the polymerizable composition, wherein the initiator component comprises an aerobic initiator. The aerobic initiator (e.g., an organoborane initiator) may be uncomplexed or complexed. Such kits are useful for bonding low surface energy substrates. For ease of application, the kits can further comprise a multi-part dispenser.
Once the parts of the kit are mixed together, bonding compositions are obtained. The compositions can be at least partially coated onto a substrate, particularly low surface energy substrates.
Once polymerized, a polymerized composition is obtained. The polymerized composition can be, for example, at least partially coated on a substrate or can be used to adhere a first and second substrate together. For example, methods of bonding at least one low surface energy substrate comprise the steps of:
providing a kit as described above,
providing a low surface energy substrate,
mixing the polymerizable composition with the initiator component to form a bonding composition;
coating at least a portion of the low surface energy substrate with the bonding composition; and
adhering the coated low surface energy substrate to a second substrate.
Advantageously, in such methods, the initiator component can be mixed in an amount that provides as little as about 0.01 weight % boron based on total weight of the bonding composition.